Why can't an iPhone 6 and a mid-2011 MacBook Air see each other in AirDrop?

I'm trying to transfer photos, for example, from an iPhone 6 running iOS 8.1.3 to a MacBook Air, mid-2011, running OS X 10.10.2.

In either of these scenarios:

• iPhone set to be discoverable by Everyone


• Finder open to AirDrop on the Mac


• Select a photo on iPhone, select Share, the Mac does not appear in the AirDrop pane

or

• iPhone set to be discoverable by Everyone


• Pick a photo on the Mac, select Share, Airdrop, no devices appear in the Send via AirDrop dialog

I have successfully used AirDrop from this Mac to other Macs in the past. Any idea why it isn't working with my iPhone? (I should point out that other features of Yosemite, such as receiving phone calls and SMS from the iPhone on the Mac, are functioning properly.)